Many designs of machines of the above described type are known in the prior art. As the machines generate a tremendous lot of dust, particularly when working in concrete, brick, rock and the like, it is important that the intake air is cleaned well before it is led into the carburettor. Therefore, a plurality of different filter systems have been developed and are in use today. In a cutting machine, which is known under its trade name Husqvarna 272K, there is a pre-filter consisting of an oiled foam plastics filter in the upper front part of the power unit, and a main filter consisting of a paper filter, which is also located in the upper past of the power unit, at the rear of the pre-filter. It is also known to clean the intake air by centrifugal cleaning in chain saws, before it is led into the carburettor. For this purpose, different nozzle (mouth piece) tubes have been developed to be mounted close to the impeller. The purification achieved by means of a centrifugal cleaner alone, however, is not sufficient for cutting machines of the type which generate large quantities of dust. In the prior art there are no cutting machines in which centrifugal cleaning is combined with further cleaning in filters.